Why Is the Ocean Salty?

By alan.raymond@weather.com

Published Sep 20 2013 03:15 AM EDT

weather.com

Earth's Primordial Ocean

The Earth began to develop water about 3.8 billion years ago. Back then, the Earth was scorching hot and water came from only a few sources: gasses emitted from below the planet’s surface and impacts from comets (a ball of solid ice and interstellar dust).

But as the Earth cooled, water vapor condensed and began to pool in valleys and low spots. These were the beginnings of our vast oceans.

Fast-forward to the present — Earth is often called the “Blue Marble,” mostly because its surface is 70 percent covered by water: 97 percent of that is salty.

Considering the Earth has a surface area of more than 123,500 acres, xxx.

What makes all that water so salty?

The answer to that question starts with a simple word: precipitation.

As rain falls it absorbs carbon in the atmosphere and on the ground: That makes the rain slightly acidic. Now a very weak form of carbonic acid, the precipitation runoff begins to interact with nearby rocks and earthy soils. The acidity in the water dissolves certain minerals, and from those minerals come elemental sodium and chloride (the ingredients of salt). Rivers and streams carry those elements out to sea, adding to the salinity (measure of saltiness) of the oceans.

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Over billions of years the process of evaporation of the oceans and resulting rain on land helped put more salts in the ocean.

Another source of salt in the ocean comes from hydrothermal vents. These vents usually occur in the middle of the ocean, along a discontinuity in the Earth’s crust. The crack allows water to seep in and become superheated from magma lurking just beneath the fissure. That superheated water permeates the surrounding rocks and dissolves minerals before being pushed back into the ocean.

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Today, for every 1,000 pounds of seawater (that’s about 117 milk jugs) there are about 22 pounds of salts.

Is the ocean still getting saltier?

Not really, according to researchers at The University of Texas, Dallas – the ocean has likely had the same salinity for more than a billion years.